The invention relates to a holder for a workpiece or a tool, in the surface of which a plurality of grooves with substantially planar flanks are made, the opposing edges of which, formed on the surface, have a predetermined spacing. Holders of this type are used for clamping for example a workpiece to be worked onto a chuck of a machine tool, for instance an electrical discharge machine.
European Patent Specification 255 042 discloses a clamping device for a tool on a machine tool which substantially comprises a chuck fastened on the machine and a holder for the tool. The holder can be released as desired from the chuck and clamped again onto the chuck by means of a clamping device. In order that the holder is always clamped onto the chuck in exactly the same position within a plane perpendicular to the clamping direction, usually the x-y plane, reference elements which interact during clamping are provided on the chuck and on the holder and include prismatic pins protruding axially from the chuck and pairs of opposing lips on the holder. The alignment of the holder in relation to the chuck is brought about by prismatic surfaces present on the prismatic pins engaging between the axially elastic lips of a pair of lips each. However, considerable outlay is involved in producing a holder of this type.
Another way of aligning the holder and chuck is disclosed by the electrode securing device according to DE-A-3003756, in which frustoconical pins projecting axially from the chuck enter prismatic grooves of the holder. Since neither the grooves nor the pins have axially elastic elements lying in between, the often considerable axial clamping forces during clamping readily lead to a permanent deformation either of the groove flanks or of the prismatic surfaces on the pins, which impairs the reproducing accuracy of the alignment of the holder in relation to the chuck.
In the document EP 1 068 919 A1, a device is presented for the position-defined clamping of a workpiece in the working area of a machine tool which has a chuck and a tool carrier. If, in preparation for the clamping, the tool carrier, provided with stepped depressions, is placed onto the chuck equipped with centering pins in such a way that an intermediate space of only a few hundredths of a millimeter remains, the centering pins butt against the inner steps of the depressions. During the subsequent clamping, the steps are elastically deformed by the centering pins. A displacement of the tool carrier between release and clamping by the chuck of only several hundredths of a millimeter under a clamping force of usually several thousand newtons requires considerable outlay to be invested in the clamping device.
The tool holder described in the document U.S. Pat. No. 5,791,803 is inexpensive to produce, but has no grooves, so that it cannot be used in a clamping system which is explained in the cited document EP-B-255 042.
The invention is based on the object of providing a workpiece or a tool holder which can be produced inexpensively and can be used primarily in the clamping system according to EP 255 042.
In the case of the holder stated at the beginning, it is provided according to the invention that the holder consists of a sintered material, at least in the region of the elastically deformable edges. This achieves an elasticity of the edges of the sintered material with respect to the clamping pressure, which on the one hand rules out the possibility of any plastic deformation of the edges or the prismatic surfaces during clamping and on the other hand nevertheless ensures excellent reproducing accuracy in the positioning of the holder in relation to the chuck. A holder of this type can be produced with relatively low costs, has high reproducing accuracy in the positioning, adequate strength and a long service life. At the same time, the chuck can develop a clamping force of approximately 4000 to approximately 8000 N on the holder.
If the holder consists entirely of sintered material, the invention can be expediently realized by using a first type of grains in the surface region, in particular in the region of the groove edges of the holder, and a second, different type of grains for the sintering for the holder core. In one embodiment of the invention, the radial grooves mentioned at the beginning are cut into the planar surface of the holder. The relatively resistant outer groove edges can axially yield elastically under the usual clamping force, on account of the softer sintering material located under them. Such a holder can therefore be successfully used in conjunction with a clamping device known from the mentioned document EP-B-255 042. The holder according to the invention is not only less expensive to produce, but also makes possible, on account of its lower weight, a reduction in the clamping force in relation to a holder consisting of solid tool steel.
The invention allows further advantageous embodiments. For instance, the sintered material may have closed pores which can deform under the clamping pressure. Alternatively, the grains of the sintered material are elastically deformable under clamping pressure. Furthermore, it may prove to be expedient to use a sintered material comprising a plurality of different types of grain, among which nonmetallic grains may also be provided, if appropriate. Furthermore, the sintered material may advantageously comprise a plurality of layers of different types of grain in each case. In addition, it proves to be expedient to give the sintered material a nonisotropic elasticity and, if appropriate, also a vibration-damping property.
For the configurations of the holder according to the invention, consisting entirely of sintered material, it proves to be expedient for special applications if a channel parallel to the respective groove extends on either side of each groove. It alternatively or additionally comes into consideration to make one or more blind holes in the sintered material, parallel to the groove flank, near to each outer groove edge.